1. Field of the Invention
The present invention relates to a general-purpose power transmission and, more particularly, to a power transmission to be incorporated into a variety of mechanisms including a mechanism, which has its drive unit and driven unit coupled to rotate relative to each other, such as: a steering wheel drive mechanism for use in various vehicles including motor cycles, bicycles, four-wheel automobiles, fork-lifts, elevation-working cars, three-wheeled buggies, three-wheeled tractors or snowmobiles of front drive, rear drive or front/rear drive type; a propelling mechanism for marine vessels; a propelling mechanism for airplanes such as V/STOLs; a spring drive mechanism for tools; a hand mechanism for robots; or an oscillating mechanism for fans or wind power plants.
2. Description of the Prior Art
A vehicle of front/rear drive type known in the prior art is exemplified by the three-wheeled buggies which are disclosed in Japanese Patent Laid-Open Nos. 157921/1985 and 181789/1986, for example. FIG. 10 is a schematic top plan view showing a front drive mechanism of such three-wheeled buggies. In this front drive mechanism of the prior art, an engine (although not shown) has its revolution transmitted through a drive chain 51, a power transmission 52 and a driven chain 53 to a front wheel 54. The power transmission 52 is constructed to include: an input shaft 55 connected to a body (although not shown); an output shaft 57 connected to a handle 56; and a synchronized ball joint 58 for coupling the two shafts 55 and 57 rotatably. Thus, even if the angle of deflection between the input shaft 55 and the output shaft 57 fluctuates as the handle 56 is steered, the synchronized ball joint 58 can still transmit the power to the front wheel 54. Although the synchronized ball joint 58 is transversely arranged, as shown in FIG. 10, similar functions could be retained even if the ball joint 58 should be so longitudinally arranged that the direction of transmission might be changed by a bevel gear.
There is also known in the prior art the motorcycle of front/rear drive type which uses a synchronized ball joint similar to that of the buggy in the power transmission to the front wheel. As the working car of front drive type, there is further known the three-wheeled tractor which has its engine mounted in the front of its body so that its handle is steered to turn the engine together with the front wheel.
Here, the power transmission 52 of the three-wheeled buggy and the motor cycle of the prior art uses the synchronized ball joint 58 so that the input shaft 55 and the output shaft 57 have to be arranged on a common line thereby to have an enlarged width. This raises a problem that a space for mounting the power transmission 52 is limited of itself. If the torque is to be increased with the handle 56 being steered, the synchronized ball joint 58 will return the output shaft 57 to the position aligned with the input shaft 55. This raises another problem that the returning force of the handle 56 is increased. Still another but important problem is that the working angle of the synchronized ball joint 58 is limited to a constant value. This makes it impossible to apply the power transmission 52 of the prior art to a mechanism in which the drive unit and the drive unit are so coupled as to rotate completely around without angular limitations. In the three-wheeled tractor of the prior art, moreover, the vibration of the engine is transmitted directly to the handle, but still the worse the steerability of the handle is deteriorated by turning the heavy engine for the steering.